Up to this point the disciples knew the Holy Spirit because Jesus had told them "for he dwelleth with you (John 14:17)." But since their names had already been "written in heaven (Luke 10:20)" when Jesus appeared to them upon His return and breathed upon them, they "received him, [and] to them gave he power to become the sons of God (John 1:12)."
Therefore, because they had been "born of the Spirit (John 3:6)", the prophecy that they would receive the Holy Spirit (John 7:39) was fulfilled since they now knew Christ no more "after the flesh (2 Corinthians 5:16)" but "in the Spirit (Romans 8:9)." "If any man have not the Spirit of Christ, he is none of his (Romans 8:9)." This is the message of salvation. "By one Spirit are we all baptized into one body...and have been all made to drink into one Spirit (1 Corinthians 12:13)." "There is one body, and one Spirit,...one Lord, one faith, [and] one baptism (Ephesians 4:4,5)."
When you are confronted with the baptism of the Holy Spirit you must know what you have to start with at salvation so you can judge what it is that is to be added and how it relates to your position as a believer. As believers, we are "one body: so also is Christ (1 Corinthians 12:12)." As members of His body, He has "blessed us with all spiritual blessings in heavenly places in Christ (Ephesians 1:3)." It is in Christ "in whom we have redemption (Ephesians 1:7)" and "in whom also we have obtained an inheritance (Ephesians 1:11)." And since it is He "in whom [we] also trusted, after that [we] heard the word of truth, the gospel of [our] salvation", it is He "in whom...[we] were sealed with that holy Spirit of promise (Ephesians 1:13)."
In other words, "by one Spirit (1 Corinthians 12:13)" we are "baptized into Christ (Galations 3:27)." We are "complete in him (Colossians 2:10)" at redemption, so the baptism of the Holy Spirit only contributes to our position as believers. These blessings are all available to the person who will "believe on his name (John 1:12)", who has been baptized into Christ, and sealed by the Holy Spirit.